In medical fields, radiation emission computed tomography (ECT: Emission Computed Tomography) apparatus is used that detects an annihilation radiation (for example, gamma rays) pair emitted from radiopharmaceutical that is administered to a subject and is localized to a site of interest for acquiring sectional images of the site of interest in the subject showing radiopharmaceutical distributions. Typical ECT equipment includes, for example, a PET (Positron Emission Tomography) device and an SPECT (Single Photon Emission Computed Tomography) device.
A PET device will be described by way of example. The PET device has a detector ring with block radiation detectors arranged in a ring shape. The detector ring is provided for surrounding a subject, and allows detection of radiation that is transmitted through the subject.
Such radiation detector arranged in the detector ring of the PET device is often equipped that allows position discrimination in a depth direction of a scintillator provided in the radiation detector for improved resolution. First, description will be given of a configuration of a conventional PET device. As shown in FIG. 10, a conventional PET device 50 includes a gantry 51 with an introducing hole that introduces a subject, a detector ring 53 having block radiation detectors 52 for detecting radiation being arranged inside the gantry 51 as to surround the introducing hole, and a support member 54 provided as to surround the detector ring 53. Each of the radiation detectors 52 has a bleeder unit 55 with a bleeder circuit. The bleeder unit 55 is provided between the support member 54 and the radiation detector 52 for connecting the support member 54 and the radiation detector 52. Such PET device is described, for example, in Patent Literature 1.
The PET device determines annihilation radiation pairs emitted from radiopharmaceutical. Specifically, an annihilation radiation pair emitted from inside of a subject M is a radiation pair having traveling directions opposite by 180 degrees. As shown in FIG. 11, the detector ring 53 has detecting elements C arranged in a z-direction for detecting an annihilation radiation pair. Accordingly, a position of the annihilation radiation pair relative to the detector ring 53 may be discriminated in the z-direction.
Description will be given of a determining method of the annihilation radiation pair in such PET device. As shown in FIG. 11, an annihilation radiation pair is generated at a vanishing point P inside the subject, and enters into two different detecting elements C of the detector ring 53. The two detecting elements independently send out two pieces of detection data D1 and D2 to an incidence time specifying section 61, where an incident time of each detection data D1, D2 into the detector ring 53 is specified.
Subsequently, the detection data D1 and D2 is outputted to a coincidence event determining section 62. The coincidence event determining section 62 determines whether incidence of radiation that the detection data D1, D2 indicates has been performed coincidentally. Where it is determined that the detection data D1, D2 has entered into the detector ring 53 coincidentally, pairing is conducted to the detection data D1, D2, and it is determined that each results from a single phenomenon of occurrence of an annihilation radiation pair. The detection data D1, D2 is sent to a detection intensity specifying section 63 and an LOR specifying section 64. The detection intensity specifying section 63 calculates intensity of incident radiation from the detection data D1 and D2. The LOR specifying section 64 specifies positional information of the detection data D1, D2. Vector data N is associated with calculated incidence time, positional information, and detection intensity. The vector data N is stored in a coincident event storage section 65 for use in generating a sectional image of the subject.
[Patent Literature 1]
Japanese Patent Publication No. 2001-194459